105_06-weathering-soil-sed_rx_part_3

105_06-weathering-soil-sed_rx_part_3 - Salt lake: formation...

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Unformatted text preview: Salt lake: formation of evaporites Salt lake: formation of evaporites Chemical and biochemical sedimentary Rocks Biogenic Biogenic – Limestone Close-up Fossils Fossils Cochina Cochina Cochina = Shell bed Chemical Sedimentary Rocks Biogenic Biogenic – Limestone Fossils Fossils Reef Reef Bora Bora Reef French Polynesia Reef Limestone El Capitan Guadalupe National Park Reef Limestone El Capitan Guadalupe National Park 1 Chemical Sedimentary Rocks Biogenic Biogenic – Limestone Chalk Chalk Chalk cliffs Dover, UK Foraminifera: Cribrohantkenima inflata 35 Ma Siliceous microfossils Chemical Sedimentary Rocks Biogenic Biogenic – Chert – NonNoncrystalline silica Diatoms: algae Radiolaria: amoeba 10 µm =0.0004 in Coal Formation Coal = biogenic sedimentary rock Coal formation 2 Coal Maturity Peat Coal Seam, Alaska Lignite Bituminous coal Anthracite Sedimentary Facies Sequence Sequence of rocks that form at the same time in different depositional environments – River ⇒ conglomerates and breccias – Beach ⇒ sandstones – Near shore/shelf ⇒ shales – Deeper marine ⇒ limestones Sedimentary Facies Coarse grained fine grained chemical sediments Reading the Story in Sedimentary Rocks Sedimentary Sedimentary Structures – – – – – Strata or beds Graded bedding Cross-bedding CrossRipple marks Mudcracks Sedimentary Structures Bedding Bedding or stratification – The most characteristic feature of sediments!!! 3 Sedimentary Structures Bedding Bedding or stratification – Principle of original horizontality Most waterMost water-laid sediment is deposited in horizontal or nearnear-horizontal layers that parallel the Earth’s surface Sedimentary Structures Bedding Bedding or stratification – Principle of Superposition younger older Sedimentary Structures CrossCross-bedding – Currents Wind Wind Water Water White Sands NP, NM – March 1998 4 Sedimentary Structures CrossCross-bedding – Currents Wind Wind Water Water Sedimentary Structures CrossCross-bedding – Wind – Wind Changes Changes direction //////////////// \\\\\\\\\\\\\\\\ //////////////// – Water Constant Constant direction //////////////// ////////////////// //////////////// Cross bedding Sedimentary Structures Graded Graded bedding: layer with a vertical change in particle size – Moving water slows down suddenly and drops the sediment load Sedimentary Structures Graded Graded bedding: Sedimentary Structures Turbidites Turbidites – Piles of sediment accumulate on continental shelf – Triggered by earthquake sediment pile becomes unstable and runs down continental slope 5 Sedimentary Structures Mudcracks Mudcracks sediment rock Sedimentary Structures Ripple Ripple marks Symmetric Symmetric Asymmetric Asymmetric Sedimentary Structures Ripple Ripple marks Sedimentary Structures Symmetric Symmetric ripple marks sediment rock Reading the Story in Sedimentary Rocks Fossils Fossils – Remains or traces of plant and animals and animal activities preserved in rocks Paleontology: Paleontology: science that deals with fossils 6 Fish Trace Fossils Trace Fossils Insects in amber Rock Formations Formation Formation – body of rock large enough to be mappable – has characteristics which distinguish it from surrounding formations – can be composed of more than one bed bed Rock Formations Contact Contact – Surface that marks the boundary between two beds or formations 7 Reading the Story in Sedimentary Rocks Determining Determining the Environment of Deposition – Geologists attempt to make interpretations about ancient environments based on analyses of rocks, fossils, and sedimentary structures and comparison with modern day processes PaleoPaleo-stuff: paleogeography, paleocurrents, paleontology, paleomagnetics Weathering, Soil, and Sedimentary Rocks Chapter 6 8 ...
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